I went to the garage, I got a razor blade and my magnetic pick up tool. The tool grabbed the razor right quick and held on tight. If all else fails, maybe silicone a magnet to a string and dip it down thru the live rock you will feel it when it hits the blade. Can you see up from under your tank with a flash light? Or maybe get over the tank with a ladder and look straight down with a flash light. I used to be a mechanic, when I first got out of the navy, and lost stuff in a engine compartment is a PITA as well. Hope you find it Charlie. If not tell Willis that if he points it out, he gets a hamburger. LOL Steve